1. Field of the Invention
The present invention relates to a screw-type hydro-extracting extruder which is especially suitable for dehydration of a substance having a relatively low liquid content.
2. Description of the Prior Art
According to conventional techniques, molding of resins containing large quantities of liquid components, such as resins formed by polymerization in the aqueous system, by a screw-type extruder is carried out after the liquid components have been removed by a pneumatic drier or fluid drier. At this drying step, since the liquid components are gasified and removed, the loss of heat is large and thermal deterioration of the resins is promoted. Recently, multi-kind but small-quantity manufacture is carried out with the same apparatus so as to obtain a variety of products from the apparatus and increase the utility value of the apparatus. When the above hydro-extracting technique is applied to this multi-kind but small-quantity manufacturing, it is expected that when one kind of a product is switched over to another kind of a product, contamination is readily caused by a minute amount of the resin left at the drying step, resulting in reduction of the productivity. In the field of rubber industries, compression dehydration has practically been adopted as means for overcoming such disadvantage. However, since the water content in a rubber composition to be dehydrated is ordinarily very high and is about 50%, a large area is required for filtration. Accordingly, there is ordinarily used a two-stage screw system in which compression dehydration is carried out in a first stage, water which is not removed by this compression dehydration is evaporated and removed by a vent mechanism disposed between the first stage and the second stage and melt molding and vulcanization is carried out in the second stage. However, this method is defective in that the structure of the dehydrating zone is complicated and the size of equipment is large. Furthermore, when this compression dehydration method is applied to raw materials having a relatively low water content, such as resins formed by polymerization in the aqueous system, the quantity of extracted water is small and merits as attained in rubber industries can hardly be attained.